Fracture energy of glass fiber reinforced cement composites: Method of determination

Based on theoretical consideration, it has been found that the fracture energy is an useful index for the evaluation of fracture toughness of GRC (Glass Fiber Reinforced Cement Composites). The method for determination of the fracture energy was proposed in this paper. Fracture energy was obtained from the work required for the fracture, i.e. the area under the load-displacement curve in a tensile test. Two notches were introduced on both sides of the specimen surface in order to obtain a stable load-displacement curve, which is necessary in determining fracture energy. The determined value did not depend on the depth of the notches if they were appropriately deep. The value, therefore, represented a property of the material, while the impact strength and critical stress intensity factor (K_IC), which are widely used as the indices of the fracture energy and fracture toughness, respectively, are not considered to be the material's properties because of the great influence of the notch depth on the indices. This paper also discusses the suitability of the present method and the error factors caused in the measurement.     

Fracture behavior of glass fiber reinforced polymer composite

Chopped strand glass fiber reinforced particle-filled polymer composite beams with varying notch-to-depth ratios and different volume fractions of glass fibers were investigated in Mode I fracture using three-point bending tests. Effects of polyester resin content and glass fiber content on fracture behavior was also studied. Polyester resin contents were used 13.00%%, 14.75%, 16.50%, 18.00% and 19.50%, and glass fiber contents were 1% and 1.5% of the total weight of the polymer composite system. Flexural strength of the polymer composite increases with increase in polyester and fiber content. The critical stress intensity factor was determined by using several methods such as initial notch depth method, compliance method and J-integral method. The values of K_IC obtained from these methods were compared.     

Fracture toughness of injection molded glass fiber reinforced polypropylene

The fracture behavior of polypropylene reinforced with 30% by weight of short glass fibers was studied using single and double feed plaque moldings. Plaques were injection molded using several gate types and gate positions. Fracture toughness K_c, was calculated at different positions in the plaque moldings using single edge notched tension specimens. Fracture toughness was assessed in the directions parallel and perpendicular to the mold fill direction through measurements of the load to produce complete fracture. Results indicated that the value of fracture toughness is affected by the type of gate as well by size of gate. Position of the specimen also affected fracture toughness. Generally, specimens taken from positions near cavity walls gave higher toughness values than those taken from the center of the moldings. Furthermore, fracture toughness in the transverse direction was consistently higher than in the melt flow direction. Finally, in the case o double feed moldings, a much higher fracture toughness was obtained when the initial crack was perpendicular to the weld line than when it was placed inside the weld line.     

Improvement of the durability of glass fiber reinforced cement using blended cement matrix

Blended cements prepared with two fly ashes were used as matrices in glass fiber reinforced cement (GRC) composites in an attempt to improve their durability. The hydrated matrices from the two blended cements investigated here had similar strength and composition. Both fly ashes reduced the Ca(OH)₂ content to the same extent but in both cases the pH level was only slightly reduced compared to the portland cement matrix. In spite of these similarities, the GRC prepared with one fly ash showed considerable improvement in durability while the other one had only a small positive effect. SEM observations indicated that the improved durability in one case was associated with modification in the microstructure of the hydration products deposited in between the glass filaments, resulting in a much more open structure compared to that of portland cement matrix or the other blended cement. It is therefore suggested that the potential of the blended cement matrix to improve the durability of GRC is associated with its ability to modify the microstructure of the paste at the glass interface. This characteristic is not necessarily related to the overall composition of the blended cement matrix and to the reactivity of fly ash with Ca(OH)₂.     

Fracture of fiber reinforced composites

Characteristics of the fracture of fiber reinforced plastic composites are described in terms of the elastic stress distribution at the crack tip, the mechanism of crack tip damage, and the modes and conditions of final fracture. The three-dimensional, stress field at the tip of a sharp crack in a laminate is presented and contrasted to traditional two-dimensional models. The response of the material in the form of inter- and intraply damage formation and growth under increasing load is characterized, and its effect in blunting the main crack is examined. The final fracture conditions, which may range from quasi-brittle to notch insensitive, are discussed and related to the damage zone extension. Observed and anticipated effects of various material and geometric parameters are also discussed.     

Microstructure of glass fibre reinforced supersulphated cement

The microstructure of one and two year old grc made from Cem-FIL alkali-resistant glass fibres and supersulphated cement has been examined using the scanning electron microscope. The structure and composition of two year old samples of supersulphated cement hydrated in a CO₂ free atmosphere is also reported. Differences in the microstructure of these cement samples and the matrix phase of the fibre composites are related to the carbonation of the composite specimens.     

Fracture and acoustic emission characteristics of glass fiber reinforced plastics panels for hot water

This study deals with the fracture process and acoustic emission (AE) characteristics of a randomly oriented E-glass fiber mat reinforcement with a crosslinked polyester. These panels were evaluated after they were immersed in hot water. The fiber volume content of the panel was 19%. Glass fiber reinforced plastics (GFRP) panels wer immersed in water at 81°C. Bending and AE monitoring tests were Performed and after bending, the cross-section of the specimen was observed by an optical microscope and SEM. The influence of degradation, due to water immersion, on the changes of fracture process of GFRP is discussed. The dominant fracture mode of the virgin specimen was matrix cracks, whereas that of the immersed specimen was debondings at the fiber bundle/matrix and fiber/matrix interfaces. This change was caused by reduction of the bonding strength at the interface. The scale of fracture can be estimated by both AE amplitude and AE energy and this estimation method was used to estimate the fracture mode changes of GFRP panels immersed in hot water.     

Properties of ceramic fiber reinforced cement composites

Mechanical properties and preliminary durability of ceramic fiber reinforced Portland cement composites tested with wet-hot accelerating method were investigated. The results showed that the flexural strength of mortar could be increased obviously by adding ceramic fiber into it, but the effect of the flexural reinforcement was influenced by various factors, including fiber length, fiber content and kinds of matrices; the preliminary durability of ceramic fiber in ordinary Portland cement tested with wet-hot accelerating method was much better than that of alkali-resistant (AR) glass fiber. The mechanism of the durability of ceramic fiber in ordinary Portland cement is also discussed.     

Short fiber reinforced thermoplastics. I. Rheological properties of glass fiber reinforced Noryl

An experimental study on the flow behavior of glass fiber reinforced Noryl (a commercial poly(phenyleneoxide)/polystyrene blend) using a capillary rheometer is described. The effect of fiber concentration on shear viscosity and die swell was studied at various temperatures. Breakage of glass fibers during flow through the rheometer is discussed; it was found that the average fiber length (about 230 μm) was not significiantly altered, except at the highest shear rate (575 s⁻¹) studied. The incorporation of short fibers into thermoplastic polymer melts increases their viscosity without changing the basic rheological character-shear rate dependency. No discernible viscosity changes were measured by incorporating 10 weight percent fibers, and upon further increase of fiber concentration from 20 to 30 weight percent no appreciable increase in viscosity was noted. It is shown that short glass fibers cause a large reduction in extrudate swell. The presence of voids and fiber orientation contribute to the decrease of the die swell, an effect greater than expected from volumetric considerations alone.     

Threaded joints in glass fiber reinforced polyamide

Threaded joints can be used to join different polymers or polymers to metals at high loads. Design with self-threading screws or threaded inserts requires dynamic mechanical properties. Results are presented on threaded joints of glass fiber reinforced polyamide 6 under static and dynamic loads. Dynamic load limits are determined by using the hysteresis measurement method with stepwise load increment experiments and single load level experiments. The failure and fatigue behavior of threaded joints is characterized by several parameters calculated from the hysteresis loop. These parameters change in a characteristic manner as a function of load and time. Significant changes exhibited by the damping and stiffness curves in stepwise load increase experiments can be used to determine the loss of preload on the screw and the beginning of screw pull out. Specially designed self threading screws for threaded joints capable of bearing high dynamic loads are discussed. These joints can attain a life in the endurance range (10⁶ cycles) without loss of preload. In comparison with S-N curves, the dynamic load limits for threaded joints can be determined more quickly by the hysteresis measurement method.     

玻璃纤维增强聚丙烯复合材料的研究进展

综述了长、短玻璃纤维增强聚丙烯（GFRPP）复合材料的研究进展,总结出纤维含量、纤维长度及分布、纤维取向及分布、纤维与基体界面结合和改性等均为影响GFRPP性能的因素。在复合材料中,长度大于临界长度的玻璃纤维对材料的强度才有作用;增强玻璃纤维与聚丙烯的界面结合也是提高增强效果的有效手段。     

炭纤维增强水泥基复合材料(CFRC)的电磁性能

炭纤维增强水泥基复合材料(Carbon Fiber Reinforced Cement Composites,CFRC)是新发展起来的一种电磁屏蔽材料,它是防止电磁污染的防护性功能材料之一。本文阐述了炭纤维增强水泥基复合材料的制备成型工艺;分析了炭纤维掺入量和长度、水灰比和密实成型制备工艺、炭纤维分散性、养护龄期、外加剂、炭纤维表面化学气相沉积(CVD)处理等因素对CFRC力学性能、导电性能、压敏性能及电磁性能的影响。合适的炭纤维掺入量和长度、炭纤维的均匀分散、合理的水灰比和炭纤维表面处理是影响CFRC导电性能和电磁性能的主要因素。CFRC对电磁波的屏蔽效果除利用屏蔽效能从反射电磁波角度衡量外,亦可从吸收电磁波角度利用反射率进行评价。     

玻纤增强热塑性塑料用阻燃剂

克来恩/Clariant公司的染料和添加剂分公司推出了2种专用于玻璃纤维增强热塑性塑料的新型阻燃剂.2种阻燃剂都是以磷酸的金属盐为基础的,不含卤化物.     

长玻璃纤维增强聚丙烯复合材料的韧性

以玻璃纤维和聚丙烯为原料,制备了长玻璃纤维增强聚丙烯(LFT-PP)复合材料,研究了基体韧性、纤维长度和界面相容剂对LFT-PP韧性的影响。结果表明LFT-PP韧性随基体韧性增加而增加;当玻璃纤维长度从2.06mm增加到4.66mm时,LFT-PP的悬臂梁缺口冲击强度从134.4J/m提高到238.0J/m,增加了约80%;添加界面改性剂降低了LFT-PP悬臂梁缺口冲击强度,从311.4J/m降为181.8J/m。     

玻纤增稿聚丙烯的研制

通用热塑性增强复合材料玻璃纤维增强聚丙烯（PP）性价比高，应用广泛。本文讨论了偶联剂、增容剂、加工工艺条件等因素对玻璃纤维增强PP性能的影响。结果表明，运用正确的偶联剂和增容剂处理玻璃纤维、增加玻璃纤维长度、适当提高玻璃纤维增强PP的挤出加工温度、适当降低挤出螺杆转速和注射速率均可提高玻纤增强PP的综合性能。     

Crystallization kinetics of glass fiber reinforced PBT composites

The effect of glass fibers on the crystallization of poly(butylene terephthalate) (PBT) was investigated by crystallization kinetics analysis under isothermal and nonisothermal conditions. From the crosspolar optical micrographs of melt‐ and solvent‐crystallized PBT composites, the glass fibers were found to increase the number density and decrease the size of crystallites. The glass fibers provided heterogeneous nucleation sites, and thus enhanced the overall rate of PBT crystallization in isothermal experiments. However, the Avrami exponent and the regime transitions were not significantly affected by the presence of glass fibers. For the nonisothermal kinetics of PBT composites, the model prediction was excellent in most ranges of crystallization, but it deviated above 70% of crystallization especially at fast cooling rates (>40°C/min). This discrepancy of the model seemed to result from the growth regime transitions, which were clearly observed especially at high undercoolings. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 576–585, 2000     

短玻纤增强ABS复合材料的研制

介绍短玻纤维增强ABS复合材料的生产工艺,实验对比了处理玻纤用偶联剂种类和加入量、玻纤含量、ABS种类及抗冲改性剂加入量对复合材料性能的影响,结果表明,玻纤用质量分数为1.5%的偶联剂KH550处理,可增强9715A ABS,同时加入质量分数为2%抗冲改性剂的可得到综合性能较好的复合材料。